When wiring and the like are formed on a substrate such as a semiconductor wafer, the substrate is required to be subjected to a fine processing and a substrate processing method using a plasma has been widely employed therefor.
The reactive ion etching (RIE) is widely employed in the field of semiconductor processing to process semiconductor devices, various substrates, composite films, and the like. Recently, a technique for narrowing a range of ion energy by increasing the frequency of RF (Radio Frequency) power and that for generating a pulsed plasma have been studied to meet the requirement for high precision of shapes of processed objects or the like.
For example, Patent Document 1 (Japanese Patent Application Publication No. 2003-234331) is one of published documents which disclose a technique for increasing RF power to a higher frequency. Patent Document 1 discloses a method for supplying two different radio frequency (RF) powers to electrodes of a parallel plate and independently controlling plasma density with a higher RF power and an average incident energy to substrate with a lower RF power in order to improve controllability of the plasma density and average incident energy to substrate. Further, Patent Document 1 discloses a technique for overlapping a higher RF power and a lower RF power in an RF electrode using an RF power supply and a matching unit for the lower RF power provided in addition to an RF power supply and a matching unit for the higher RF power.
Non-Patent Document 1 (J. Appl. Phys. Vol 86 No2 643 (2000)) is an example of published documents which disclose techniques for generating pulsed plasma. Non-Patent Document 1 discloses a technique for generating a pulsed plasma in a substrate processing method using a plasma, in which a plasma-generating gas is prevented from being dissociated by performing a pulse control of RF power for plasma generation.
In addition, there has been known a technique for controlling an average incident energy to substrate in a pulsing manner by applying a lower frequency RF power in the form of a pulse.
Further, there has been known a combination of the technique of generating a pulsed plasma by applying a higher frequency RF power in the form of a pulse and the technique of controlling the average incident energy to substrate in a pulsing manner by applying a lower frequency RF power in the form of a pulse.
However, in such a substrate processing method, if a balance is disturbed between an ON/OFF control of a RF power supply for plasma generation (hereinafter referred to as “excitation power applying device”) and an ON/OFF control of a RF power supply for bias (hereinafter referred to as “bias power applying device”), an amplitude (Vpp) of bias RF power may become excessively large, which may result in abnormal discharge and/or damage of an RF matching part of a matching unit, thereby making it difficult to perform a stable substrate process.